In applications involving wireless transmission of data between first and second electronic devices, one or more of the following issues can be important:                There is limited available bandwidth and the need for upstream data streaming from the first to the second device prevents the use of bandwidth for down stream data.        The second devices have transmitters, which are low powered in comparison with the first devices, providing asymmetrical transmission range. Thus the transmission range from the first to the second devices is longer than the range from the second to the first devices.        Power is an issue on the second device, requiring the transmitter of that device to be kept off whenever possible.        The first device is a transmit-only device, which cannot receive.        The second device is a receive-only device, which cannot transmit.        
Such properties are e.g. important for wireless applications targeted towards listening devices, such as hearing aids, as they are physically very limited in size. The size causes a range of problems when applying wireless technologies to e.g. hearing aids, where the most significant are:                Limited power budget, for both transmission and reception        Relatively small antennas (low Rx-sensitivity and Tx-efficiency)        
WO 2007/046748 discloses a system for assisting a hearing impaired user, the system comprising a transmitter and receiver adapted to convey data representing audio to a user. The audio data may originate from a microphone, a speaker, a TV, a telephone, etc. The transmitter device may be configured to transmit control signals while continuing to transmit audio data (e.g. using another radio channel or by time multiplexing with the audio data).
WO 2007/052189 discloses a hearing aid system aiming at allowing a user himself to adapt the gain characteristics, etc. of a hearing aid device to his personal needs. In a specific control mode, the hearing aid device is configured to, during a control signal detection period, be programmed by control signals embedded in audio signals.
US 2005/0255843 A1 describes a wireless communication protocol, e.g. for an inductive link.
U.S. Pat. No. 6,424,820 B1 describes a short range inductively coupled wireless communication system employing analogue FM for transmitting stereo audio from a control unit to a pair of ear pieces.